At one foot from the front panel, Xserve's sound pressure level registered a fairly steady 60 dBA, and around back, 65 dBA. This is not an acoustic breakthrough when compared to the PowerPC-driven Xserve G5 or to two-socket Netburst Xeon servers. EPA guidelines set 80 dBA as the danger threshold for workers without hearing protection, so a single Xserve's fan noise falls well within the safe range. Even so, it highlights the importance of protecting your hearing in the server room. If you can't have a conversation without shouting, your environment is dangerously loud.
The new Xserve does not share a key quality with Xserve G5: The fan noise is not decreased by disabling one of the CPUs. Xserve G5 gets markedly quieter, but then, the PowerPC 970 CPU has more on-board peripherals. Shutting down a socket took bus drivers with it, while Intel's x86 busses are all external.
Xserve's exterior thermal profile strikes me as mostly average for a modern Intel x86 1U rack server. At the back panel, I measured peak temperatures of 118 degrees F, while the front panel ran only a few degrees above room temperature. The system's forced-air cooling is very effective. I was troubled by one focused hot spot of 108 degrees on the top cover, at least ten degrees hotter than the average for that surface in a room at exactly 78 degrees. High radiated heat is potentially hazardous for the equipment in the space above the heated device. It's harder for air conditioning to remove, and it's usually symptomatic of inadequate heat sinking. That may be something that Apple will address in a future design. However, the toaster on Xserve's system board, Intel's Core microarchitecture north bridge (front-side bus controller) chip, isn't something that Apple can easily chill. It runs as much as 60 degrees Fahrenheit hotter than the CPUs. In fact, it's hotter by a wide margin than any other component according to Apple's sensor data. Apple can convert this from radiated heat to forced-air heat, but its burden on power and cooling will remain.
Thank you and goodnight
I have referred throughout this story to the plethora of sensors inside Xserve. One of the delights of OS X Server is the simple, yet deep management and monitoring tools that come with it. Sensors and tools are not new to Apple. What is new is that sensor reports and management tools now operate whether the system's power is on or not, and whether you're on the same subnet as the server's Ethernet ports or not. The magic is lights-out management, long a feature demanded by Intel x86 server buyers but absent in Apple servers. Now, Apple has equipped Xserve with a standards-based baseboard management controller that operates continuously as long as AC power is available. The BMC draws negligible power when Xserve is off, making it very UPS-friendly, and you can reboot, power down and power up Xserve from anywhere. These operations previously required that OS X boot successfully, but an OS that won't boot is a pretty common reason for an administrator's Blackberry to buzz.